1. Field of the Invention
The present invention relates to a display device using polymer dispersed liquid crystal as a liquid crystal layer, and to a camera using the display device.
2. Description of the Related Art
A liquid crystal panel is used as an image display unit for various usages because the panel has features such as thinness and low power consumption. A twist nematic mode has been known as a general alignment mode of a liquid crystal layer in a liquid crystal panel. A liquid crystal panel of the foregoing alignment mode has a structure in which a liquid crystal layer is held between two polarizers in order to control a quantity of light transmitting through a liquid crystal panel. However, there is a problem that the polarizer has a high light absorption factor; as a result, a light available efficiency is low.
In order to solve the foregoing problem, the following liquid crystal panel has attracted interest as a liquid crystal panel which has no need to provide a polarizer for controlling a quantity of transmitted light. In the liquid crystal panel, for example, polymer dispersed liquid crystal such as a polymer network (hereinafter, referred to simply as PN) liquid crystal disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2003-270657 is used as a liquid crystal layer. PN liquid crystal is formed by dispersing liquid crystal in polymer such as PN. The liquid crystal panel using the foregoing PN liquid crystal as a liquid crystal layer changes the alignment state of a liquid crystal molecule between the following two states. One is a state in which a degree of light scattering becomes high, and the other is a state in which a degree of light scattering is reduced. In this way, it is possible to control the quantity of light transmitting through a liquid crystal panel toward a predetermined direction.
FIG. 20 is a view to explain an alignment state of a liquid crystal molecule when a degree of light scattering of a liquid crystal layer is high (light scattering state) in a liquid crystal panel using a PN liquid crystal as a liquid crystal layer. FIG. 21 is a view to explain an alignment state of a liquid crystal molecule when a degree of light scattering of a liquid crystal layer is reduced (light non-scattering state) in a liquid crystal panel using a PN liquid crystal as a liquid crystal layer (the case where a dielectric constant anisotropy of a liquid crystal molecule is positive).
A liquid crystal panel using a PN liquid crystal as a liquid crystal layer has a first substrate 51 formed of a transparent insulating material such as glass and a second substrate 53 formed of the same material as above. For example, a conductive film formed of a transparent conductive material such as indium tin oxide (ITO) is provided as a display electrode 52 on the first substrate 51. Moreover, a conductive film formed of a transparent conductive material such as ITO is provided as a common electrode 54 on the second substrate 53. The first substrate 51 is stuck to the second substrate 53 via a gap material (seal) so that the display electrode 52 faces the common electrode 54 and a predetermined gap is formed between the first and second substrates 51 and 53. In the gap between the first and second substrates 51 and 53, PN liquid crystal in which liquid crystal molecules 56 are dispersed in PN is sealed to form a liquid crystal layer.
The potential of the display electrode 52 and the potential of the common electrode 54 are set to an equal potential, and thereby, control is carried out so that a voltage applied to a liquid crystal layer formed of PN liquid crystal becomes 0V. In this case, as can be seen from FIG. 20, liquid crystal molecules 56 dispersed in the ON 55 are in an alignment state of being turned to an arbitrary direction at random. When light 57 passes through a liquid crystal layer of the foregoing alignment state, the light 57 passes through a plurality of regions having a mutually different refractive index. For this reason, the light 57 passes through the liquid crystal layer while being dispersed. Therefore, a scattering degree of light transmitting through the liquid crystal panel becomes high; as a result, the liquid crystal panel is visible as a cloudy state (dark state). The foregoing PN 55 reduces an alignment regular force between liquid crystal molecules 56 so that the alignment of liquid crystal molecules is made at random. Namely, the PN 55 acts so that a degree of light scattering becomes high.
Conversely, the potential of the display electrode 52 and the potential of the common electrode 54 are set to a mutually different potential, and thereby, control is carried out so that a voltage applied to a liquid crystal layer formed of ON liquid crystal becomes sufficiently high. In this case, as can he seen from FIG. 21, liquid crystal molecules 56 are in an alignment state in which their parallel direction is uniquely arranged to the thickness direction of the liquid crystal layer. In the liquid crystal layer of the foregoing alignment state, a refractive index becomes unique in the liquid crystal layer. Therefore, a degree of scatting of the light 57 transmitting through the liquid crystal layer is reduced. As a result, the liquid crystal panel is visible as a transparent state. In order to improve a transparent state, the refractive index of PN 55 is set to become equal to an apparent refractive index of liquid crystal molecules in the foregoing state.
As described above, the liquid crystal panel using PN liquid crystal as a liquid crystal layer has the following features. Namely, the alignment of liquid crystal molecules dispersed in PN 55 is changed between the following two states by controlling each potential of display electrode 52 and common electrode 54 arranged via a liquid crystal layer. One is a state in which a degree of light scattering becomes high, and the other is a state in which a degree of light scattering is reduced. Therefore, it is possible to control a quantity of light transmitting through a liquid crystal panel toward a predetermined direction.
If a liquid crystal panel is provided with a plurality of segments, a display area of a first substrate is provided with a plurality of segment electrodes functioning as a display electrode. First and second substrate are arranged so that these segment electrodes commonly orient with respect to one common electrode, which is formed on the entire surface of a second substrate. Moreover, each of segment electrodes is formed so that the potential is individually set. A liquid crystal layer of a region corresponding to one segment electrode is defined as one segment. A voltage applied to a liquid crystal layer is controlled for each segment.
As described above, a plurality of segments is provided, and polymer dispersed liquid crystal is used as a liquid crystal layer. However, in this case, there is a problem that a gap between neighboring two segment electrodes is visible as a cloudy region (dark region).